Polyphenylene ether has been used in a wide variety of applications because it is excellent in dimensional stability as well as mechanical and electrical properties and heat resistance. However, polyphenylene ether has a significant drawback that it is by itself poor in oil resistance and molding workability. In order to overcome this drawback, there has been proposed a technique to prepare a material in which a polyamide is blended with a polyphenylene ether, and such materials are nowadays used in an extremely wide variety of applications (Patent Document 1).
Recently, polyamide-polyphenylene ether resin compositions have been used in large-size molded products such as automotive fenders. When such molded products are used in combination with metal parts, high temperature environments cause troubles such as dimensional discrepancies and deformation caused by contact with metal parts because the molded products are too larger in linear expansion coefficient than the metal parts. Accordingly, there have been generally adopted such techniques in which an inorganic filler is blended with the resin composition in order to reduce the linear expansion coefficient of the resin composition. However, such blending has resulted in a problem that the impact resistance of the resin composition is remarkably degraded.
As techniques to reduce linear expansion coefficient and to improve Izod impact value, attempts have been made in which a small platy inorganic filler having an average particle size of 8 μm or less, in particular, 5 μm or less is blended with a polyamide-polyphenylene ether resin composition. Disclosed examples of such techniques include: a technique blending talc having an average particle size of 5 μm or less and an aspect ratio of 5 or more (Patent Document 2); a technique blending a platy inorganic filler having an average particle size of 5 μm or less and an aspect ratio of 3 or more (Patent Document 3); a technique blending a platy inorganic filler having an average particle size of 3 μm or less and a specific particle size distribution (Patent Document 4); a technique blending a platy filler having an average particle size of 1.2 to 5 μm and an L/D value of 3 or more and/or a fibrous inorganic filler having a fiber length of 2 μm or more, carbon black, fine fibrous carbon and a hydrogenated block copolymer having a number average molecular weight of 80,000 or less (Patent Document 5); a technique blending talc and carbon (Patent Document 6); a technique blending an inorganic filler having an average particle size of 8 μm or less and a hydrogenated block copolymer having a number average molecular weight of 50,000 to 180,000 (Patent Document 7); and a technique blending small-particle-size talc having an average particle size of 1 to 4 μm and large-particle-size talc having an average particle size of 5 to 10 μm (Patent Document 8).
However, because a platy inorganic filler having a small average particle size has a large surface area, the use of such a filler results in a remarkable degradation of flowability, in particular, a degradation of flowability in a thin mold. Additionally, the above-mentioned conventional techniques do not sufficiently improve tensile elongation.
Recently, application of polyamide-polyphenylene ether resin compositions filled with an inorganic filler and a conductive material to large-size thin-wall molded products such as automotive outer panels has come under review. In particular, the improvement of dart impact strength based on falling weight or the like and flowability in a thin mold, and the impartment of conductivity have come to be demanded.
As affairs now stand, in view of such demands from the market, the above-mentioned conventional techniques are poor in the balance between dart impact strength, tensile elongation and flowability, and have not yet reached a practical application level to be sufficiently satisfactory. Accordingly, resin compositions having excellent balance between dart impact strength, flowability and linear expansion coefficient, and additionally, having conductivity have long been awaited.
Patent Document 1: JP-B-45-997 (corresponding to U.S. Pat. No. 3,379,792)
Patent Document 2: JP-A-2-163158 (corresponding to U.S. Pat. No. 5,086,105)
Patent Document 3: JP-A-6-145499 (corresponding to U.S. Pat. No. 5,475,049)
Patent Document 4: JP-A-2002-194206
Patent Document 5: JP-A-2002-194207
Patent Document 6: JP-A-2003-528941 (corresponding to European Patent EP1,232,218)
Patent Document 7: JP-A-2004-285136
Patent Document 8: JP-A-5-220826